Purification and spectroscopic characterization of beta-amyloid precursor protein from porcine brains.
Soluble and membrane-bound isoforms of beta-amyloid protein precursor (APP) of Alzheimer's disease were extracted and purified from porcine brains. At least three types of soluble APP and membrane-bound APP with different molecular masses, ranging from 86 kDa to 116 kDa, were obtained. CD and infrared spectroscopies were used to determine the overall secondary-structure content of APP. The infrared spectra of soluble and membrane-bound APP (in dry and hydrated states) were similar in the amide-I and amide-II regions, suggesting that the overall secondary structures of the soluble and membrane isoforms were roughly identical. The amide-I band is composed of at least five component bands, located at 1694, 1674, 1652, 1637 and 1618 cm(-1) for soluble APP, and located at 1687, 1674, 1651, 1637 and 1614-1606 cm(-1) for membrane-bound APP, as evidenced by their respective second-derivative infrared spectra. The 1651-1652-cm(-1) band was associated with alpha-helix structures, while two types of beta-sheet structures are evidenced by two characteristic pairs of component bands. The 1674-cm(-1) and 1637-cm(-1) bands for soluble APP and membrane-bound APP were tentatively associated to beta-sheet structures. The second pair of bands, located at 1694 cm(-1) and at 1618 cm(-1) for soluble APP and at 1687 cm(-1) and 1614-1606 cm(-1) for membrane-bound APP, were associated with intermolecular beta-sheet structures or aggregated strands, as confirmed by heat denaturation. CD spectra indicated the presence of alpha-helix structures in soluble and membrane-bound APP. The secondary-structure content, estimated from CD spectra, was about 40-45% alpha-helix and 15-20% beta-sheet structures for soluble and membrane-bound APP.
de La Fournière-Bessueille
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Université Claude Bernard Lyon I, CNRS UPRESA 5013, Laboratoire de Physico-Chimie Biologique, Villeurbanne, France.
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Buchet
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D000544:Alzheimer Disease / Q000378:metabolism; D016564:Amyloid beta-Protein Precursor / Q000737:chemistry* / Q000145:classification / Q000302:isolation & purification; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002942:Circular Dichroism; D004591:Electrophoresis, Polyacrylamide Gel; D008565:Membrane Proteins / Q000737:chemistry; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared; D013552:Swine
D016564:Amyloid beta-Protein Precursor; D008565:Membrane Proteins